Shift register

ABSTRACT

A shift register comprises a plurality of stages, {S n }, n=1, 2, . . . , N, N being a positive integer. In one embodiment, each stage S n  includes a pull-up circuit having an input for receiving one of a first clock signal, CK 1 , and a second clock signal, XCK 1 , an output for responsively outputting an output signal, O n , and an input node Q n , a pull-up control circuit electrically coupled to the input node Q n  and configured such that when receiving a first input signal, the pull-up control circuit responsively generates a signal that is provided to the input node Q n  to turn on the pull-up circuit, a pull-down circuit electrically coupled to the input node Q n  and configured to provide a first voltage to one of the input node Q n  and the output of the pull-up circuit, and a pull-down control circuit configured to receive one of a third clock signal, CK 2 , and a fourth clock signal, XCK 2 , and responsively generate the first voltage to turn on the pull-down circuit of the stage S n  and the pull-down circuit of one of the stage S n−1  and the stage S n+1 .

FIELD OF THE INVENTION

The present invention relates generally to a shift register, and inparticular to a shift register having a plurality of stages with eachpair of stages sharing a single pull-down control circuit.

BACKGROUND OF THE INVENTION

A liquid crystal display (LCD) includes an LCD panel formed with liquidcrystal cells and pixel elements with each associating with acorresponding liquid crystal cell. These pixel elements aresubstantially arranged in the form of a matrix having gate lines in rowsand data lines in columns. The LCD panel is driven by a driving circuitincluding a gate driver and a data driver. The gate driver generates aplurality of gate signals (scanning signals) sequentially applied to thegate lines for sequentially turning on the pixel elements row-by-row.The data driver generates a plurality of source signals (data signals),i.e., sequentially sampling image signals, simultaneously applied to thedata lines in conjunction with the gate signals applied to the gatelines for aligning states of the liquid crystal cells on the LCD panelto control light transmittance therethrough, thereby displaying an imageon the LCD.

In such a driving circuit, a shift register is utilized in the gatedriver to generate the plurality of gate signals for sequentiallydriving the gate lines. To lower down costs, there have been efforts tointegrate the shift register and the gate driver into an LCD panel. Oneof the efforts, for example, is to fabricate the shift register and thegate driver on a glass substrate of the LCD panel, namely, the gate onarray (GOA) arrangement, using amorphous silicon (a-Si) thin filmtransistors (TFTs), and/or low temperature polycrystalline silicon(LTPS) TFTs.

Generally, a shift register having multiple stages is designed such thatin operation there are some TFTs that are turned on for a long period oftime for the purpose of discharges. Additionally, such a shift registeris usually supplied with two or more clock signals to substantiallyshift an output signal of a stage from its input signal that is anoutput signal of its immediately prior stage, thereby generating of aplurality of sequentially shifted output signals. If the two or moreclock signals have a same frequency that is very high, some TFTs in theshift register may frequently be turned on during operation. However,when voltages are continually or frequently applied to TFTs made froma-Si and/or LTPS material for a long period of time, the characteristicsof the TFTs may deteriorate due to stress thereon and thus the TFTs maynot function properly, thereby reducing the reliability of the shiftregister. For the shift register operating reliably and normally, aplurality of pull-down circuit sets is applied to reduce the stress.This makes the GOA design of an LCD panel very complicate.

Therefore, a heretofore unaddressed need exists in the art to addressthe aforementioned deficiencies and inadequacies.

SUMMARY OF THE INVENTION

The present invention, in one aspect, relates to a shift register. Inone embodiment, the shift register includes a plurality of stages,{S_(n)}, n=1, 2, . . . , N, N being a positive integer. Each stage S_(n)comprises a first input, IN1, for receiving one of a first clock signal,CK1, and a second clock signal, XCK1, a second input, IN2, for receivinga third clock signal, CK2, if the first input IN1 receives the firstclock signal CK1, or a fourth clock signal, XCK2, if the first input IN1receives the second clock signal XCK1, a third input, IN3, for receivinga supply voltage, VSS, a fourth input, IN4, a fifth input, IN5, a sixthinput, IN6, a seventh input, IN7, and an eighth input, IN8.

Furthermore, each stage S_(n) comprises a first output, OUT1, foroutputting an output signal, O_(n), and a second output, OUT2, foroutputting a pull-down signal, K_(n).

Moreover, each stage S_(n) comprises a pull-up circuit electricallycoupled between the first input IN1 and the first output OUT1, a pull-upcontrol circuit electrically coupled between the fifth inputs IN5 andthe pull-up circuit, a first pull-down circuit electrically coupled tothe pull-up circuit, a first pull-down control circuit electricallycoupled to the second input IN2, the second output OUT2, and the firstpull-down circuit, a second pull-down circuit electrically coupled tothe fourth input IN4, the first pull-down control circuit and thepull-up circuit; and a third pull-down circuit electrically coupled tothe sixth input IN6, and the second pull-down circuit and the pull-upcircuit.

The plurality of stages {S_(n)} is electrically coupled in serial. Insuch an arrangement, the fourth input IN4 of the n-th stage S_(n) iselectrically coupled to the second output OUT2 of the (n−1)-th stageS_(n−1), for receiving a corresponding pull-down output signal K_(n−1)therefrom, or the second output OUT2 of the (n+1)-th stage S_(n+1), forreceiving a corresponding pull-down output signal K_(n+1) therefrom. Thefifth input IN5 of the n-th stage S_(n) is electrically coupled to thefirst output OUT1 of the (n−1)-th stage S_(n−1), for receiving acorresponding output signal O_(n−1) therefrom. The sixth input IN6 ofthe n-th stage S_(n) is electrically coupled to the first output OUT1 ofthe (n+1)-th stage S_(n+1), for receiving a corresponding output signalO_(n+1) therefrom. The seventh input IN7 of the n-th stage S_(n) iselectrically coupled to the first output OUT1 of the (n+2)-th stageS_(n+2), for receiving a corresponding output signal O_(n+2) therefrom.The eighth input IN8 of the n-th stage S_(n) is electrically coupled tothe first output OUT1 of the (n−2)-th stage S_(n−2), for receiving acorresponding output signal O_(n−2) therefrom.

Additionally, the shift register also has a first clock signal line forproviding the first clock signal, CK1, a second clock signal line forproviding the second clock signal, XCK2, a third clock signal line forproviding the third clock signal, CK1, a fourth clock signal line forproviding the forth clock signal, XCK2, and a reference line forproviding a supply voltage, VSS.

In one embodiment, each of the first, second, third and fourth clocksignals is characterized with a frequency and a phase. The frequency ofthe first clock signal and the frequency of the second clock signal aresubstantially identical and the phase of the first clock signal and thephase of the second clock signal are substantially reversed. Thefrequency of the third clock signal and the frequency of the fourthclock signal are substantially identical and the phase of the thirdclock signal and the phase of the fourth clock signal are substantiallyreversed, respectively. In one embodiment, the frequency of the firstclock signal is higher than the frequency of the third clock signal.

In one embodiment, the pull-up control circuit comprises a firsttransistor T1 having a gate electrically coupled to the fifth input IN5,a source electrically coupled to the gate and a drain.

The pull-up circuit comprises a second transistor T2 having a gateelectrically coupled to the drain of the first transistor T1 of thepull-up control circuit, a source electrically coupled to the firstinput IN1 and a drain electrically coupled to the first output OUT1, andat least one capacitor electrically coupled between the source and thedrain of the second transistor T2.

The first pull-down control circuit comprises a fourth transistor T4having a gate electrically coupled to the second input IN2, a sourceelectrically coupled to the gate and a drain electrically coupled to thesecond output OUT2, and an eighth transistor T8 having a gateelectrically coupled to the gate of the second transistor T2 of thepull-up circuit, a source electrically coupled to the drain of thefourth transistor T4 and a drain electrically coupled to the referenceline.

The first pull-down circuit comprises a sixth transistor T6 having agate electrically coupled to the drain of the fourth transistor T4 ofthe first pull-down control circuit, a source electrically coupled tothe gate of the second transistor T2 of the pull-up circuit and a drainelectrically coupled to the drain of the second transistor T2 of thepull-up circuit, and a seventh transistor T7 having a gate electricallycoupled to the drain of the fourth transistor T4 of the first pull-downcontrol circuit, a source electrically coupled to the drain of thesecond transistor T2 of the pull-up circuit and a drain electricallycoupled the reference line.

The second pull-down circuit comprises a ninth transistor T9 having agate electrically coupled to the fourth input IN4, a source electricallycoupled to the drain of the second transistor T2 of the pull-up circuitand a drain electrically coupled the reference line, a tenth transistorT10 having a gate electrically coupled to the fourth input IN4, a sourceelectrically coupled to the gate of the second transistor T2 of thepull-up circuit and a drain electrically coupled to the drain of thesecond transistor T2 of the pull-up circuit, and an eleventh transistorT11 having a gate electrically coupled to the gate of the secondtransistor T2 of the pull-up circuit, a source electrically coupled tothe fourth input IN4 and a drain electrically coupled the referenceline.

The third pull-down circuit comprises a twelfth transistor T12 having agate electrically coupled to the sixth input IN6, a source electricallycoupled to the gate of the second transistor T2 of the pull-up circuitand a drain electrically coupled the reference line; and a thirteenthtransistor T13 having a gate electrically coupled to the sixth inputIN6, a source electrically coupled to the drain of the second transistorT2 of the pull-up circuit and a drain electrically coupled the referenceline.

Additionally, each stage S_(n) further comprises a third transistor T3having a gate electrically coupled to the seventh input IN7, a sourceelectrically coupled to the reference line and a drain electricallycoupled to the drain of the first transistor T1 of the pull-up controlcircuit, and a fifth transistor T5 having a gate electrically coupled tothe eighth input IN8, a source electrically coupled to the referenceline and a drain electrically coupled to the drain of the firsttransistor T1 of the pull-up control circuit.

In another aspect, the present invention relates to a shift registerthat includes a plurality of stages, {S_(n)}, n=1, 2, . . . , N, N beinga positive integer.

Each stage S_(n) includes a first input, IN1, for receiving one of afirst clock signal, CK1, and a second clock signal, XCK1, a secondinput, IN2, for receiving a third clock signal, CK2, if the first inputIN1 receives the first clock signal CK1, or a fourth clock signal, XCK2,if the first input IN1 receives the second clock signal XCK1, a thirdinput, IN3, for receiving a supply voltage, VSS, a fourth input, IN4,for receiving a fourth input signal, a fifth input, IN5, for receiving afifth input signal, a sixth input, IN6, for receiving a sixth inputsignal, a first output, OUT1, for outputting an output signal, O_(n),and a second output, OUT2, for outputting a pull-down signal, K_(n).

Each stage S_(n) also includes a pull-up circuit electrically coupledbetween the first input IN1 and the first output OUT1, a pull-up controlcircuit electrically coupled between the fifth inputs IN5 and thepull-up circuit, a first pull-down circuit electrically coupled to thepull-up circuit, a first pull-down control circuit electrically coupledto the second input IN2, the second output OUT2, and the first pull-downcircuit, a second pull-down circuit electrically coupled to the fourthinput IN4, the first pull-down control circuit and the pull-up circuit,and a third pull-down circuit electrically coupled to the eighth inputIN8, the second pull-down circuit and the pull-up circuit. In oneembodiment, the fourth input signal is corresponding to one of thepull-down signal K_(n−1) of the (n−1)-th stage S_(n−1) and the pull-downsignal K_(n+1) of the (n+1)-th stage S_(n+1), wherein the fifth inputsignal is corresponding to the output signal O_(n−1) of the (n−1)-thstage S_(n−1), and wherein the sixth input signal is corresponding tothe output signal O_(n+1) of the (n+1)-th stage S_(n+1).

In one embodiment, the pull-up control circuit comprises a firsttransistor T1 having a gate electrically coupled to the fifth input IN5,a source electrically coupled to the gate and a drain.

The pull-up circuit comprises a second transistor T2 having a gateelectrically coupled to the drain of the first transistor T1 of thepull-up control circuit, a source electrically coupled to the firstinput IN1 and a drain electrically coupled to the first output OUT1, andat least one capacitor electrically coupled between the source and thedrain of the second transistor T2.

The first pull-down control circuit comprises a fourth transistor T4having a gate electrically coupled to the second input IN2, a sourceelectrically coupled to the gate and a drain electrically coupled to thesecond output OUT2, and an eighth transistor T8 having a gateelectrically coupled to the gate of the second transistor T2 of thepull-up circuit, a source electrically coupled to the drain of thefourth transistor T4 and a drain configured to receive the supplyvoltage VSS.

The first pull-down circuit comprises a sixth transistor T6 having agate electrically coupled to the drain of the fourth transistor T4 ofthe first pull-down control circuit, a source electrically coupled tothe gate of the second transistor T2 of the pull-up circuit and a drainelectrically coupled to the drain of the second transistor T2 of thepull-up circuit, and a seventh transistor T7 having a gate electricallycoupled to the drain of the fourth transistor T4 of the first pull-downcontrol circuit, a source electrically coupled to the drain of thesecond transistor T2 of the pull-up circuit and a drain configured toreceive the supply voltage VSS.

The second pull-down circuit comprises a ninth transistor T9 having agate electrically coupled to the fourth input IN4, a source electricallycoupled to the drain of the second transistor T2 of the pull-up circuitand a drain configured to receive the supply voltage VSS, a tenthtransistor T10 having a gate electrically coupled to the fourth inputIN4, a source electrically coupled to the gate of the second transistorT2 of the pull-up circuit and a drain electrically coupled to the drainof the second transistor T2 of the pull-up circuit, and an eleventhtransistor T11 having a gate electrically coupled to the gate of thesecond transistor T2 of the pull-up circuit, a source electricallycoupled to the fourth input IN4 and a drain configured to receive thesupply voltage VSS.

The third pull-down circuit comprises a twelfth transistor T12 having agate electrically coupled to the sixth input IN6, a source electricallycoupled to the gate of the second transistor T2 of the pull-up circuitand a drain configured to receive the supply voltage VSS, and athirteenth transistor T13 having a gate electrically coupled to thesixth input IN6, a source electrically coupled to the drain of thesecond transistor T2 of the pull-up circuit and a drain configured toreceive the supply voltage VSS

Also, each stage S₁, comprises a seventh input, IN7, for receiving aseventh input signal, an eighth input, IN8, for receiving a eighth inputsignal, a third transistor T3 having a gate electrically coupled to theseventh input IN7, a source configured to receive the supply voltage VSSand a drain electrically coupled to the drain of the first transistor T1of the pull-up control circuit, and a fifth transistor T5 having a gateelectrically coupled to the eighth input IN8, a source configured toreceive the supply voltage VSS and a drain electrically coupled to thedrain of the first transistor T1 of the pull-up control circuit. Theseventh input signal is corresponding to the output signal O_(n+2) ofthe (n+2)-th stage S_(n+2). The eighth input signal is corresponding tothe output signal O_(n−2) of the (n−2)-th stage S_(n−2).

In yet another aspect, the present invention relates to a shift registercomprising a plurality of stages, {S_(n)}, n=1, 2, . . . , N, N being apositive integer. In one embodiment, each stage S_(n) comprises apull-up circuit having an input for receiving one of a first clocksignal, CK1, and a second clock signal, XCK1, an output for responsivelyoutputting an output signal, O_(n), and an input node Q_(n), a pull-upcontrol circuit electrically coupled to the input node Q_(n) of thepull-up circuit and configured such that when receiving a first inputsignal, the pull-up control circuit responsively generates a signal thatis provided to the input node Q_(n) of the pull-up circuit to turn onthe pull-up circuit, a pull-down circuit electrically coupled to theinput node Q_(n) of the pull-up circuit and configured to provide afirst voltage to one of the input node Q_(n) and the output of thepull-up circuit, a pull-down control circuit configured to receive oneof a third clock signal, CK2, and a fourth clock signal, XCK2, andresponsively generate the first voltage to turn on the pull-down circuitof the stage S_(n) and the pull-down circuit of one of the stage S_(n−1)and the stage S_(n+1), and a key pull-down circuit configured to receivea second input signal. The first input signal is corresponding to theoutput signal O_(n−1) of the stage S_(n−1), and the second input signalis corresponding to the output signal O_(n+1) of the stage S_(n+1).

In one embodiment, the pull-up circuit 1010 comprises a first transistorT1 having a gate electrically coupled to the input node Q_(n), a sourceelectrically coupled to the input for receiving one of the first clocksignal CK1 and the second clock signal XCK1 and a drain electricallycoupled to the output for outputting the output signal O_(n).

The pull-up control circuit 1020 comprises a third transistor T3 havinga gate, a source electrically coupled to the output of the stage S_(n−1)for receiving the output signal O_(n−1) therefrom and a drainelectrically coupled to the input node Q_(n) of the pull-up circuit1010, and a fourth transistor T4 having gate electrically coupled to theinput node Q_(n−1) of the pull-up circuit of the stage S_(n−1), a sourceconfigured to receive the second clock signal XCK1 if the input of thepull-up circuit receives the first clock signal CK1 or the first clocksignal CK1 if the input of the pull-up circuit receives the second clocksignal XCK1 and a drain electrically coupled to the gate of the thirdtransistor T3.

The pull-down control circuit comprises a seventh transistor T7 having agate configured to receive a third clock signal CK2, a sourceelectrically coupled to the gate and a drain electrically coupled to anode K, an eighth transistor T8 having a gate electrically coupled tothe input node Q_(n−1) of the pull-up circuit of the stage S_(n−1), asource electrically coupled to the node K and a drain configured toreceive a supply voltage VSS, and a ninth transistor T9 having a gateelectrically coupled to the input node Q_(n) of the pull-up circuit, asource electrically coupled to the node K and a drain configured toreceive the supply voltage VSS.

The pull-down circuit comprises a thirteenth transistor T13 having agate electrically coupled to the node K of the pull-down controlcircuit, a source electrically coupled to the input node Q_(n) and adrain configured to receive the supply voltage VSS; and a fourteenthtransistor T14 having a gate electrically coupled to the node K of thepull-down control circuit, a source electrically coupled to the outputof the pull-up circuit and a drain configured to receive the supplyvoltage VSS.

The key pull-down circuit comprises a twenty-first transistor T21 havinga gate electrically coupled to the output of the stage S_(n+1) forreceiving the output signal O_(n+1) therefrom, a source electricallycoupled to the input node Q_(n) of the pull-up circuit and a drainconfigured to receive the supply voltage VSS, and a twenty-secondtransistor T22 having a gate electrically coupled to the output of thestage S_(n+1) for receiving the output signal O_(n+1) therefrom, asource electrically coupled to the output of the pull-up circuit and adrain configured to receive the supply voltage VSS.

Additionally, each stage S_(n) also comprises a twenty-fifth transistorT25 having a gate configured to receive the output signal O_(n−2) of the(n−2)-th stage S_(n−2), a source configured to receive the supplyvoltage VSS and a drain electrically coupled to the input node Q_(n) ofthe pull-up circuit; and a twenty-sixth transistor T26 having a gateconfigured to receive the output signal O_(n+2) of the (n+2)-th stageS_(n+2), a source configured to receive the supply voltage VSS and adrain electrically coupled to the input node Q_(n) of the pull-upcircuit.

In a further aspect, the present invention relates to a shift register.In one embodiment, the shift register has a plurality of stages,{S_(n)}, n=1, 2, . . . , N, N being a positive integer. Each stage S_(n)includes a pull-up circuit having an input for receiving a correspondingclock signal Cn, an output for responsively outputting an output signal,O_(n), and an input node, Q_(n), between the input and the output, apull-up control circuit electrically coupled to the input node Q_(n) ofthe pull-up circuit 810 and configured such that when receiving a firstinput signal, the pull-up control circuit responsively generates asignal that is identical to the first input signal and is provided tothe input node Q_(n) of the pull-up circuit to turn on the pull-upcircuit, a first pull-down circuit electrically coupled to the inputnode Q_(n) and the output of the pull-up circuit and configured toreceive a pull-down signal K_(n), a second pull-down circuitelectrically coupled to the input node Q_(n) and the output of thepull-up circuit, and configured to receive a second input signal, athird pull-down circuit electrically coupled to the input node Q_(n) andthe output of the pull-up circuit and configured to receive a thirdinput signal, and a first pull-down control circuit configured toreceive a fourth input signal and responsively generate the pull-downsignal K_(n) that is provided to the first pull-down circuit of thestage S₁, and the second pull-down circuit of one of the stage S_(n−1)and the stage S_(n+1), respectively.

In one embodiment, each of the clock signals {Cn}, n=1, 2, 3, . . . , N,is characterized with a frequency and a phase, wherein the frequenciesof the clock signals {Cn} are substantially identical, and the phases ofthe clock signals {Cn} are sequentially shifted, respectively.

The second input signal is corresponding to the pull-down signal K_(n−1)of the stage S_(n−1) or the pull-down signal K_(n+1) of the stageS_(n+1), and the third input signal is corresponding to the outputsignal O_(n+2) of the stage S_(n+2),

In one embodiment, the first input signal is corresponding to the outputsignal O_(n−1) of the stage S_(n−1) for n=2, 3, 4, . . . , N, or a startsignal for n=1. In another embodiment, the first input signal iscorresponding to the output signal O_(n−2) of the stage S_(n−2) for n=3,4, 5, . . . , N, or a start signal for n=1 and 2. In an alternativeembodiment, the first input signal is corresponding to a start signal.

These and other aspects of the present invention will become apparentfrom the following description of the preferred embodiment taken inconjunction with the following drawings, although variations andmodifications therein may be affected without departing from the spiritand scope of the novel concepts of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate one or more embodiments of theinvention and, together with the written description, serve to explainthe principles of the invention. Wherever possible, the same referencenumbers are used throughout the drawings to refer to the same or likeelements of an embodiment, and wherein:

FIG. 1 shows a block diagram of a shift register according to oneembodiments of the present invention;

FIG. 2 shows a block diagram of a shift register according to anotherembodiments of the present invention;

FIG. 3 shows a GOA architecture of a shift register according to oneembodiment of the present invention;

FIG. 4 shows a circuit diagram of two neighboring stages of a shiftregister according to one embodiment of the present invention;

FIG. 5 shows a timing chart of input and output signals of the shiftregister as shown in FIG. 4;

FIG. 6 shows a GOA architecture of a shift register according to anotherembodiment of the present invention;

FIG. 7 shows a circuit diagram of two neighboring stages of a shiftregister according to another embodiment of the present invention;

FIG. 8 shows a GOA architecture of a shift register according to oneembodiment of the present invention;

FIG. 9 shows a circuit diagram of two neighboring stages of a shiftregister according to one embodiment of the present invention;

FIG. 10 shows a timing chart of input and output signals of the shiftregister as shown in FIG. 9;

FIG. 11 shows a block diagram of a shift register according to oneembodiments of the present invention;

FIG. 12 shows a circuit diagram of two neighboring stages of a shiftregister according to another embodiment of the present invention;

FIG. 13 shows a timing chart of input and output signals of the shiftregister as shown in FIG. 12;

FIG. 14 shows a block diagram of a shift register according to oneembodiments of the present invention;

FIG. 15 shows a circuit diagram of two neighboring stages of a shiftregister according to another embodiment of the present invention;

FIG. 16 shows a block diagram of a shift register according to oneembodiments of the present invention;

FIG. 17 shows a circuit diagram of two neighboring stages of a shiftregister according to another embodiment of the present invention;

FIG. 18 shows a timing chart of input and output signals of the shiftregister as shown in FIG. 17;

FIG. 19 shows a block diagram of a shift register according to oneembodiments of the present invention; and

FIG. 20 shows a circuit diagram of two neighboring stages of a shiftregister according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is more particularly described in the followingexamples that are intended as illustrative only since numerousmodifications and variations therein will be apparent to those skilledin the art. Various embodiments of the invention are now described indetail. Referring to the drawings, like numbers indicate like componentsthroughout the views. As used in the description herein and throughoutthe claims that follow, the meaning of “a”, “an”, and “the” includesplural reference unless the context clearly dictates otherwise. Also, asused in the description herein and throughout the claims that follow,the meaning of “in” includes “in” and “on” unless the context clearlydictates otherwise.

The description will be made as to the embodiments of the presentinvention in conjunction with the accompanying drawings in FIGS. 1-20.In accordance with the purposes of this invention, as embodied andbroadly described herein, this invention, in one aspect, relates to ashift register with embedded bidirectional scanning function.

Referring in general to FIG. 1, a shift register 100 is shown accordingto one embodiment of the present invention. The shift register includesa first clock signal line 111 for providing the first clock signal, CK1,a second clock signal line 112 for providing the second clock signal,XCK2, a third clock signal line 113 for providing the third clocksignal, CK1, a fourth clock signal line 114 for providing the forthclock signal, XCK2, and a reference line 115 for providing a supplyvoltage, VSS.

In one embodiment, each of the first, second, third and fourth clocksignals, CK1, XCK1, CK2 and XCK2 is characterized with a frequency and aphase. The frequency of the first clock signal CK1 and the frequency ofthe second clock signal XCK1 are substantially identical and the phaseof the first clock signal CK1 and the phase of the second clock signalXCK1 are substantially reversed. The frequency of the third clock signalCK2 and the frequency of the fourth clock signal XCK2 are substantiallyidentical and the phase of the third clock signal CK2 and the phase ofthe fourth clock signal XCK2 are substantially reversed, respectively.In one embodiment, the frequency of the first clock signal CK1 is higherthan the frequency of the third clock signal CK2.

The shift register 100 includes a plurality of stages, {S_(n)}, n=1, 2,. . . , N, N being a positive integer.

Each stage S_(n) has a first input, IN1, for receiving one of a firstclock signal, CK1, and a second clock signal, XCK1, a second input, IN2,for receiving a third clock signal, CK2, if the first input IN1 receivesthe first clock signal CK1, or a fourth clock signal, XCK2, if the firstinput IN1 receives the second clock signal XCK1, a third input, IN3, forreceiving a supply voltage, VSS, a fourth input, IN4, a fifth input,IN5, a sixth input, IN6, a seventh input, IN7, and an eighth input, IN8.

Each stage S_(n) also has a first output, OUT1, for outputting an outputsignal, O_(n), and a second output, OUT2, for outputting a pull-downsignal, K_(n).

The plurality of stages {S_(n)} is electrically coupled in serial. Asshown in FIG. 1, the fourth input IN4 of the n-th stage S_(n) iselectrically coupled to the second output OUT2 of the (n+1)-th stageS_(n+1), for receiving a corresponding pull-down output signal K_(n+1)therefrom. The fifth input IN5 of the n-th stage S_(n) is electricallycoupled to the first output OUT1 of the (n−1)-th stage S_(n−1), forreceiving a corresponding output signal O_(n−1) therefrom. The sixthinput IN6 of the n-th stage S_(n) is electrically coupled to the firstoutput OUT1 of the (n+1)-th stage S_(n+1), for receiving a correspondingoutput signal O_(n+1) therefrom. The seventh input IN7 of the n-th stageS_(n) is electrically coupled to the first output OUT1 of the (n+2)-thstage S_(n+2), for receiving a corresponding output signal O_(n+2)therefrom. The eighth input IN8 of the n-th stage S_(n) is electricallycoupled to the first output OUT1 of the (n−2)-th stage S_(n−2), forreceiving a corresponding output signal O_(n−2) therefrom.

FIG. 2 shows a shift register 200 according to another embodiment of thepresent invention. The shift register 200 has the same design as theshift register 100, except that the fourth input IN4 of the n-th stageS_(n) is electrically coupled to the second output OUT2 of the (n−1)-thstage S_(n−1), for receiving a corresponding pull-down output signalK_(n−1) therefrom.

FIG. 3 shows schematically a GOA architecture of a shift register 300according to one embodiment of the present invention. The shift register300 has multiple stages {S_(n)} that are deposited/formed on a glasssubstrate (not shown). FIG. 3 shows only four stages S_(n), S_(n+1),S_(n+2), and S_(n+3). Each stage has a pull-up control circuit 320 and apull-up circuit 310 formed adjacent to the pull-up control circuit 320on the glass substrate along a first row 380. Each stage also has afirst pull-down control circuit 340, a first pull-down circuit 330, asecond pull-down circuit 350 and a key pull-down circuit 360 formed onthe substrate, in turn, along a second row 390 that is adjacent to thefirst row 380.

Depending upon which the first, second, third and fourth clock signals,CK1, XCK1, CK2 and XCK2 are input into a stage, the first pull-downcontrol circuit 340 can be a CK pull-down control circuit or an XCKpull-down control circuit; the first pull-down circuit 330 can be a CKpull-down circuit or an XCK pull-down circuit; and the second pull-downcircuit 350 can be an XCK pull-down control circuit or a CK pull-downcircuit. For example, if the first and third clock signals CK1 and CK2are respectively input into the first and second inputs IN1 and IN2 of astage, for example, stage S_(n), the first pull-down control circuit340, the first pull-down circuit 330 and the second pull-down circuit350 are corresponding to a CK pull-down control circuit, a CK pull-downcircuit and an XCK pull-down control circuit, respectively. If thesecond and fourth clock signals XCK1 and XCK2 are respectively inputinto the first and second inputs IN1 and IN2 of a stage, for example,stage S_(n+1), the first pull-down control circuit 340, the firstpull-down circuit 330 and the second pull-down circuit 350 arecorresponding to an XCK pull-down control circuit, an XCK pull-downcircuit and a CK pull-down control circuit, respectively.

For such a design, a single pull-down control circuit 340 is utilized tocontrol the first pull-up circuit of the stage S_(n), and a pull-upcircuit of the stage S_(n−1).

Referring to FIG. 4, a circuit diagram of two neighboring stages S_(n)and S_(n+1) of the shift register 300 is shown. Each stage S_(n)includes a first input IN1 for receiving one of the first clock signalCK1 and the second clock signal XCK, a second input IN2 for receivingthe third clock signal CK2 if the first input IN1 receives the firstclock signal CK1, or the fourth clock signal XCK2 if the first input IN1receives the second clock signal XCK1, a third input IN3 for receivingthe supply voltage VSS a fourth input IN4 for receiving a fourth inputsignal, a fifth input IN5 for receiving a fifth input signal, a sixthinput IN6 for receiving a sixth input signal, a first output OUT1 foroutputting an output signal O_(n), and a second output OUT2 foroutputting a pull-down signal K_(n).

Each stage S_(n) includes a pull-up circuit 310, a pull-up controlcircuit 320, a first pull-down circuit 330, a first pull-down controlcircuit 340, a second pull-down circuit 350 a third pull-down circuit360. The pull-up circuit 310 is electrically coupled between the firstinput IN1 and the first output OUT1. The pull-up control circuit 320 iselectrically coupled between the fifth inputs IN5 and the pull-upcircuit 310. The first pull-down circuit 330 is electrically coupled tothe pull-up circuit 310. The first pull-down control circuit 340 iselectrically coupled to the second input IN2, the second output OUT2,and the first pull-down circuit 330. The second pull-down circuit 350 iselectrically coupled to the fourth input IN4, the first pull-downcontrol circuit 340 and the pull-up circuit 310. The third pull-downcircuit 360 electrically coupled to the eighth input IN8, the secondpull-down circuit 350 and the pull-up circuit 310. As shown in FIG. 3,the fourth input signal is corresponding to the pull-down signal K_(n+1)of the (n+1)-th stage S_(n+1). The fifth input signal is correspondingto the output signal O_(n−1) of the (n−1)-th stage S_(n−1). The sixthinput signal is corresponding to the output signal O_(n+1) of the(n+1)-th stage S_(n+1).

Specifically, the pull-up control circuit 320 has a first transistor T1having a gate electrically coupled to the fifth input IN5 for receivingthe output signal O_(n−1) of the stage S_(n−1), a source electricallycoupled to the gate and a drain electrically coupled to a node Q.

The pull-up circuit 310 has a second transistor T2 having a gateelectrically coupled to the node Q_(n) a source electrically coupled tothe first input IN1 for receiving the first clock signal CK1 or thesecond clock signal XCK1, and a drain electrically coupled to the firstoutput OUT1 for outputting an stage output signal O_(n) in response tothe received first clock signal CK1 or second clock signal XCK1 in thesource. Additionally, the pull-up circuit 310 also has twoserial-connected capacitors are electrically coupled between the sourceand the drain of the second transistor T2.

The first pull-down control circuit 340 has a fourth transistor T4having a gate electrically coupled to the second input IN2 for receivingthe third clock signal CK2 if the source of the second transistor T2receives the first clock signal CK1 or the fourth clock signal XCK2 ifthe source of the second transistor T2 receives the second clock signalXCK1, a source electrically coupled to the gate and a drain electricallycoupled to the second output OUT2 for outputting the pull-down signalK_(n), which is provided to the second pull-down circuit 350 of thestage S_(n+1) or S_(n−1). The first pull-down control circuit 340 alsohas an eighth transistor T8 having a gate electrically coupled to thenode Q that is eclectically connected to the gate of the secondtransistor T2 of the pull-up circuit 310, a source electrically coupledto the drain of the fourth transistor T4 and a drain configured toreceive the supply voltage VSS.

The first pull-down circuit 330 includes a sixth transistor T6 and aseventh transistor T7. The sixth transistor T6 has a gate electricallycoupled to the drain of the fourth transistor T4 of the first pull-downcontrol circuit 340, a source electrically coupled to the node Q or thegate of the second transistor T2 of the pull-up circuit 310 and a drainelectrically coupled to the drain of the second transistor T2 of thepull-up circuit 310 which is electrically connected to the first outputOUT1. The seventh transistor T7 having a gate electrically coupled tothe drain of the fourth transistor T4 of the first pull-down controlcircuit 340, a source electrically coupled to the drain of the secondtransistor T2 of the pull-up circuit 310 and a drain configured toreceive the supply voltage VSS.

The second pull-down circuit 350 has a ninth transistor T9, a tenthtransistor T10 and an eleventh transistor T11. The ninth transistor T9has a gate electrically coupled to the fourth input IN4 for receivingthe pull-down signal K_(n+1) of the stage S_(n+1) or the pull-downsignal K_(n+1) of the stage S_(n−1), a source electrically coupled tothe drain of the second transistor T2 of the pull-up circuit 310 and adrain configured to receive the supply voltage VSS. The tenth transistorT10 has a gate electrically coupled to the fourth input IN4 forreceiving the pull-down signal K_(n+1) of the stage S_(n+1) or thepull-down signal K_(n+1) of the stage S_(n−1), a source electricallycoupled to the node Q or the gate of the second transistor T2 of thepull-up circuit 310 and a drain electrically coupled to the drain of thesecond transistor T2 of the pull-up circuit 310. The eleventh transistorT11 has a gate electrically coupled to the gate of the second transistorT2 of the pull-up circuit 310, a source electrically coupled to thefourth input IN4 and a drain configured to receive the supply voltageVSS.

The third pull-down circuit 360 has a twelfth transistor T12 and athirteenth transistor T13. The twelfth transistor T12 has a gateelectrically coupled to the sixth input IN6 for receiving the outputsignal O_(n+1) of the stage S_(n+1), a source electrically coupled tothe node Q or the gate of the second transistor T2 of the pull-upcircuit 310 and a drain configured to receive the supply voltage VSS.The thirteenth transistor T13 has a gate electrically coupled to thesixth input IN6 or receiving the output signal O_(n+1) of the stageS_(n+1), a source electrically coupled to the drain of the secondtransistor T2 of the pull-up circuit 310 and a drain configured toreceive the supply voltage VSS.

Also, each stage S_(n) include a seventh input, IN7 for receiving aseventh input signal, an eighth input, IN8, for receiving a eighth inputsignal, a third transistor T3 and a fifth transistor T5. The seventhinput signal is corresponding to the output signal O_(n+2) of the(n+2)-th stage S_(n+2). The eighth input signal is corresponding to theoutput signal O_(n−2) of the (n−2)-th stage S_(n−2). The thirdtransistor T3 has a gate electrically coupled to the seventh input IN7,a source configured to receive the supply voltage VSS and a drainelectrically coupled to the drain of the first transistor T1 of thepull-up control circuit 320. The fifth transistor T5 has a gateelectrically coupled to the eighth input IN8, a source configured toreceive the supply voltage VSS and a drain electrically coupled to thedrain of the first transistor T1 of the pull-up control circuit 320.

When the first clock signal CK1 and the second clock signal XCK1 arerespectively input into the first input IN1 and the second input IN2,the first pull-down control circuit 340, the first pull-down circuit330, the second pull-down circuit 350, and the third pull-down circuit360 are corresponding to the CK pull-down control circuit, the CKpull-down circuit, XCK pull-down circuit and Key pull-down circuit shownin FIG. 3, respectively. Otherwise, when the third clock signal CK2 andthe fourth clock signal XCK2 are respectively input into the first inputIN1 and the second input IN2, the first pull-down control circuit 340,the first pull-down circuit 330, the second pull-down circuit 350, andthe third pull-down circuit 360 are corresponding to the XCK pull-downcontrol circuit, the XCK pull-down circuit, CK pull-down circuit and Keypull-down circuit shown in FIG. 3, respectively.

FIG. 5 shows a timing chart of input and output signals for the shiftregister as shown in FIG. 4. The first, second, third and fourth clocksignals, CK1, XCK1, CK2 and XCK2 are the input signals. Each of thefirst, second, third and fourth clock signals, CK1, XCK1, CK2 and XCK2is characterized with a frequency and a phase. The frequency of thefirst clock signal CK1 and the frequency of the second clock signal XCK1are substantially identical and the phase of the first clock signal CK1and the phase of the second clock signal XCK1 are substantiallyreversed. The frequency of the third clock signal CK2 and the frequencyof the fourth clock signal XCK2 are substantially identical and thephase of the third clock signal CK2 and the phase of the fourth clocksignal XCK2 are substantially reversed, respectively. In the exemplaryembodiment, the frequency of the first clock signal CK1 is higher thanthe frequency of the third clock signal CK2.

Signals O_(n) and O_(n−1) are respectively the output signals from thestages S_(n) and S_(n−1), in response to the input signals received inthe stages S_(n) and S_(n−1). Signal K1 is the pull-down signal outputfrom the second output OUT2 of the stage S_(n−1) or S_(n+1). SignalsQ_(n) and Q_(n+1) are the voltage at the node Q of the stages S_(n) andS_(n+1), respectively.

FIG. 6 shows schematically a GOA architecture of a shift register 400according to another embodiment of the present invention. The GOAarchitecture of the shift register 400 is same as that of the shiftregister 300 shown in FIG. 3, except that a single CK/XCK pull-downcontrol circuit is used to control the CK/XCK pull-up circuit of thestage S_(n), and a XCK/CK pull-up circuit of the stage S_(n+1).

FIG. 7 shows a circuit diagram of two neighboring stages S_(n) andS_(n+1) of the shift register 400. The circuit diagram is same as thatof the shift register 300 shown in FIG. 4, except that the fourth inputsignal is corresponding to the pull-down signal K_(n−1) of the (n−1)-thstage S_(n−1).

Referring to FIG. 8, a GOA architecture of a shift register 500 is shownaccording to yet another embodiment of the present invention.

A circuit diagram of a pair of two neighboring stages S_(n) and S_(n+1)of the shift register 500 is shown in FIG. 9. The pair of stages S_(n)and S_(n+1) includes pull-up circuits 510 a and 510 b, pull-up controlcircuits 420 a and 520 b, pull-down control circuits 540 a and 540 b,pull-down circuits 530 a, 530 b, 530 c and 530 d, and key pull-downcircuits 560 a and 560 b.

Specifically, the pull-up circuit 510 a has a first transistor T1 havinga gate electrically coupled to the input node Q_(n), a sourceelectrically coupled to the input for receiving the first clock signalCK1 and a drain electrically coupled to the output for outputting theoutput signal O_(n). The pull-up circuit 510 b has a first transistor T2having a gate electrically coupled to the input node Q_(n+1), a sourceelectrically coupled to the input for receiving the second clock signalXCK1 and a drain electrically coupled to the output for outputting theoutput signal O_(n+1).

The pull-up control circuit 520 a includes a third transistor T3 and afourth transistor T4. The third transistor T3 has a gate, a sourceelectrically coupled to the output of the stage S_(n−1) for receivingthe output signal O_(n−1) therefrom and a drain electrically coupled tothe input node Q_(n) or the gate of the pull-up circuit 510 a. Thefourth transistor T4 has a gate electrically coupled to the input nodeQ_(n−1) of the stage S_(n−1), a source configured to receive the secondclock signal XCK1 and a drain electrically coupled to the gate of thethird transistor T3. The pull-up control circuit 520 b includes a fifthtransistor T5 and a sixth transistor T6. The fifth transistor T5 has agate, a source electrically coupled to the output of the stage S_(n) forreceiving the output signal O_(n) therefrom and a drain electricallycoupled to the input node Q_(n+1) or the gate of the pull-up circuit 510b. The sixth transistor T6 has a gate electrically coupled to the inputnode Q_(n) of the stage S_(n), a source configured to receive the firstclock signal CK1 and a drain electrically coupled to the gate of thefifth transistor T5.

The pull-down control circuit 540 a comprises a seventh transistor T7,an eighth transistor T8 and a ninth transistor T9. The seventhtransistor T7 has a gate configured to receive the third clock signalCK2, a source electrically coupled to the gate and a drain electricallycoupled to a node K. The eighth transistor T8 has a gate electricallycoupled to the input node Q_(n+1) or the gate of the second transistorT2 of the pull-up circuit 510 b of the stage S_(n+1), a sourceelectrically coupled to the node K and a drain configured to receive asupply voltage VSS. The ninth transistor T9 has a gate electricallycoupled to the input node Q_(n), a source electrically coupled to thenode K and a drain configured to receive the supply voltage VSS. Thepull-down control circuit 540 b includes a tenth transistor T10, aneleventh transistor T11 and a twelfth transistor T12. The tenthtransistor T10 has a gate configured to receive the fourth clock signalXCK2, a source electrically coupled to the gate and a drain electricallycoupled to a node P. The eleventh transistor T11 has a gate electricallycoupled to the input node Q_(n+1) or the gate of the second transistorT2 of the pull-up circuit 510 b of the stage S_(n+1), a sourceelectrically coupled to the node P and a drain configured to receive asupply voltage VSS. The twelfth transistor T12 has a gate electricallycoupled to the input node Q_(n) or the gate of the first transistor T1of the pull-up circuit 510 a of the stage S_(n), a source electricallycoupled to the node P and a drain configured to receive the supplyvoltage VSS.

The pull-down circuit 530 a has a thirteenth transistor T13 and afourteenth transistor T14. The thirteenth transistor T13 has a gateelectrically coupled to the node K of the pull-down control circuit 540a, a source electrically coupled to the input node Q_(n) and a drainconfigured to receive the supply voltage VSS. The fourteenth transistorT14 has a gate electrically coupled to the node K of the pull-downcontrol circuit 540 a, a source electrically coupled to the output ofthe pull-up circuit 510 a and a drain configured to receive the supplyvoltage VSS.

The pull-down circuit 530 b has a fifteenth transistor T15 and asixteenth transistor T16. The fifteenth transistor T15 has a gateelectrically coupled to the node K of the pull-down control circuit 540a, a source electrically coupled to the input node Q_(n+1) and a drainconfigured to receive the supply voltage VSS. The sixteenth transistorT16 has a gate electrically coupled to the node K of the pull-downcontrol circuit 540 a, a source electrically coupled to the output ofthe pull-up circuit 510 b and a drain configured to receive the supplyvoltage VSS.

The pull-down circuit 530 c has a seventeenth transistor T17 and aneighteenth transistor T18. The seventeenth transistor T17 has a gateelectrically coupled to the node P of the pull-down control circuit 540b, a source electrically coupled to the input node Q_(n) of the stageS_(n) and a drain. The eighteenth transistor T18 has a gate electricallycoupled to the node P of the pull-down control circuit 540 b, a sourceelectrically coupled to the input node of the stage S_(n+1) or receivingthe output signal O_(n+1) therefrom and a drain electrically coupled tothe drain of the seventeenth transistor T17.

The pull-down circuit 530 d has a nineteenth transistor T19 and atwentieth transistor T20. The nineteenth transistor T19 has a gateelectrically coupled to the node P of the pull-down control circuit 540b, a source electrically coupled to the output Q_(n) of the stage S_(n)and a drain configured to receive the supply voltage VSS. The twentiethtransistor T20 has a gate electrically coupled to the node P of thepull-down control circuit 540 b, a source electrically coupled to theoutput of the stage S_(n+1) or receiving the output signal O_(n+1)therefrom and a drain configured to receive the supply voltage VSS.

The key pull-down circuit 560 a includes a twenty-first transistor T21and a twenty-second transistor T22. The twenty-first transistor T21 hasa gate electrically coupled to the output of the stage S_(n+1) forreceiving the output signal O_(n+1) therefrom, a source electricallycoupled to the input node Q_(n) of the stage S_(n) and a drainconfigured to receive the supply voltage VSS. The twenty-secondtransistor T22 has a gate electrically coupled to the output of thestage S_(n+1) for receiving the output signal O_(n+1) therefrom, asource electrically coupled to the output of the pull-up circuit 510 afor receiving the output signal O_(n) therefrom and a drain configuredto receive the supply voltage VSS.

The key pull-down circuit 560 b includes a twenty-third transistor T23and a twenty-fourth transistor T24. The twenty-third transistor T23 hasa gate electrically coupled to the output of the stage S_(n+2) forreceiving the output signal O_(n+2) therefrom, a source electricallycoupled to the gate of the sixteenth transistor T16 of the pull-downcircuit 530 b and a drain configured to receive the supply voltage VSS.The twenty-fourth transistor T24 has a gate electrically coupled to theoutput of the stage S_(n+2) for receiving the output signal O_(n+2)therefrom, a source electrically coupled to the output of the stageS_(n+1) for receiving the output signal O_(n+1) therefrom and a drainconfigured to receive the supply voltage VSS.

Additionally, the stage S_(n) also includes a twenty-fifth transistorT25 and a twenty-sixth transistor T26. The twenty-fifth transistor T25has a gate configured to receive the output signal O_(n−2) of the(n−2)-th stage S_(n−2), a source configured to receive the supplyvoltage VSS and a drain electrically coupled to the input node Q_(n) orthe gate of the first transistor T1 of the pull-up circuit 510 a. Thetwenty-sixth transistor T26 has a gate configured to receive the outputsignal O_(n+2) of the (n+2)-th stage S_(n+2), a source configured toreceive the supply voltage VSS and a drain electrically coupled to theinput node Q_(n) or the gate of the first transistor T1 of the pull-upcircuit 510 a. The stage S_(n+1) also includes a twenty-seventhtransistor T27 and a twenty-eighth transistor T28. The twenty-seventhtransistor T27 has a gate configured to receive the output signalO_(n+3) of the (n+3)-th stage S_(n−2), a source configured to receivethe supply voltage VSS and a drain electrically coupled to the inputnode Q_(n+1) or the gate of the first transistor T2 of the pull-upcircuit 510 b. The twenty-eighth transistor T28 has a gate configured toreceive the output signal O_(n−1) of the (n−1)-th stage S_(n−1), asource configured to receive the supply voltage VSS and a drainelectrically coupled to the input node Q_(n+1) or the gate of the firsttransistor T2 of the pull-up circuit 510 b.

FIG. 10 shows a timing chart of input and output signals for the shiftregister 500 shown in FIG. 9. The first, second, third and fourth clocksignals, CK1, XCK1, CK2 and XCK2 are the input signals. Signals O_(n)and O_(n−1) are respectively the output signals from the stages S_(n)and S_(n−1), in response to the input signals received in the stagesS_(n) and S_(n−1). Signals K and P is the voltage at the node K and P,respectively. Signals Q_(n) and Q_(n+1) are the voltage at the nodeQ_(n) of the stages S_(n) and the node Q_(n+1) of the stages S_(n+1),respectively.

Referring to FIG. 11, a shift register 600 is shown schematicallyaccording to one embodiment of the present invention. The shift register600 has a plurality of stages, {S_(n)}, n=1, 2, . . . , N, where N canbe any integer greater than 1. The plurality of stages {S_(n)} iselectrically connected in serial. In FIG. 11, only the first to fourthstages S₁, S₂, S₃ and S₄ of the shift register 600 are shown. Each ofthe stages S₁, S₂, S₃ and S₄ is configured to receive a correspondingclock signal, C1, C2, C3 or C4, and a supply voltage, VDDa or VDDb, andresponsively output an output signal, O₁, O₂, O₃ or O₄. Furthermore,each stage S_(n) is also configured to receive the output signal O_(n−1)of the stage S_(n−1) and the output signal O_(n+2) of the stage S_(n+2).For example, the stage S₂ is electrically connected to the stage S₁ andthe stage S₂ for receiving the output signals O1 and O4 therefrom,respectively. For the first stage S₁, a start signal, ST, is appliedthereto. Additionally, each stage S₁, S₂, S₃ or S₄ also outputs acorresponding pull-down signal K₁, K₂, K₃ or K₄, that is provided to itsimmediately next stage.

FIG. 12 shows a circuit diagram of the first and second stages S₁, S₂ ofa shift register 700 according to one embodiment of the presentinvention. Each stage S₁ or S₂ includes a pull-up circuit 710, a pull-upcontrol circuit 720, a first pull-down circuit 730, a second pull-downcircuit 750, a third pull-down circuit 760 and a first pull-down controlcircuit 740 electrically coupled to each other.

For the stage S₁, the pull-up circuit 710 is configured to receive afirst clock signal C1 and responsively output an output signal, O₁. Thepull-up control circuit 720 is configured such that when receiving thestart signal ST, the pull-up control circuit 720 generates a signal thatis provided to the pull-up circuit 710 to turn on the pull-up circuit710. The first pull-down control circuit 740 is configured to receivethe first supply voltage signal VDDa and responsively generate thepull-down signal K₁ that is provided to the first pull-down circuit 730of this stage, and the second pull-down circuit 750 of the next stageS₂, respectively. The third pull-down circuit 760 of the stage S₁ isconfigured to receive the output signal O₃ of the stage S₃.

For the stage S₂, the pull-up circuit 710 is configured to receive asecond clock signal C2 and responsively output an output signal, O₂. Thepull-up control circuit 720 is configured such that when receiving theoutput signal O₁ of the stage S₁, the pull-up control circuit 720generates a signal that is provided to the pull-up circuit 710 to turnon the pull-up circuit 710. The first pull-down control circuit 740 isconfigured to receive the second supply voltage signal VDDb andresponsively generate the pull-down signal K₂ that is provided to thefirst pull-down circuit 730 of this stage, and the second pull-downcircuit 750 of the next stage S₃, respectively. The second pull-downcircuit 750 of the stage S₂ is configured to receive the pull-downsignal K₁ of the stage S₁. The third pull-down circuit 760 is configuredto receive the output signal O₄ of the stage S₄.

Specifically, for the stage S₁, the pull-up control circuit 720 has afirst transistor T1 having a gate adapted for receiving the start pulseST, a source electrically coupled to the gate and a drain electricallycoupled to the node Q₁, as shown in FIG. 12.

The pull-up circuit 710 has a second transistor T2 having a gateelectrically coupled to the node Q₁, a source adapted for receiving thefirst clock signal C1, and a drain electrically coupled to the outputfor outputting the stage output signal O₁ in response to the receivedfirst clock signal C1 in the source. Additionally, the pull-up circuit710 also has two serial-connected capacitors are electrically coupledbetween the source and the drain of the second transistor T2.

The first pull-down control circuit 740 has a fourth transistor T4having a gate adapted for receiving the first supply voltage signalVDDa, a source electrically coupled to the gate and a drain adapted foroutputting the pull-down signal K₁, which is provided to the secondpull-down circuit 750 of the stage S₂. The first pull-down controlcircuit 740 also has an eighth transistor T8 having a gate electricallycoupled to the node Q₁ that is eclectically connected to the gate of thesecond transistor T2 of the pull-up circuit 710, a source electricallycoupled to the drain of the fourth transistor T4 and a drain configuredto receive the supply voltage VSS.

The first pull-down circuit 730 includes a sixth transistor T6 and aseventh transistor T7. The sixth transistor T6 has a gate electricallycoupled to the drain of the fourth transistor T4 of the first pull-downcontrol circuit 740, a source electrically coupled to the node Q₁ or thegate of the second transistor T2 of the pull-up circuit 710 and a drainelectrically coupled to the drain of the second transistor T2 of thepull-up circuit 710. The seventh transistor T7 has a gate electricallycoupled to the drain of the fourth transistor T4 of the first pull-downcontrol circuit 740, a source electrically coupled to the drain of thesecond transistor T2 of the pull-up circuit 710 and a drain configuredto receive the supply voltage VSS.

The second pull-down circuit 750 has a ninth transistor T9, a tenthtransistor T10 and an eleventh transistor T11. The ninth transistor T9has a gate, a source electrically coupled to the drain of the secondtransistor T2 of the pull-up circuit 710 and a drain configured toreceive the supply voltage VSS. The tenth transistor T10 has a gate, asource electrically coupled to the node Q₁ or the gate of the secondtransistor T2 of the pull-up circuit 710 and a drain electricallycoupled to the drain of the second transistor T2 of the pull-up circuit710. The eleventh transistor T11 has a gate electrically coupled to thegate of the second transistor T2 of the pull-up circuit 710, a sourceelectrically coupled to the fourth input IN4 and a drain configured toreceive the supply voltage VSS.

The third pull-down circuit 760 has a twelfth transistor T12 and athirteenth transistor T13. The twelfth transistor T12 has a gate adaptedfor receiving the output signal O₃ of the stage S₃, a sourceelectrically coupled to the node Q₁ or the gate of the second transistorT2 of the pull-up circuit 710 and a drain configured to receive thesupply voltage VSS. The thirteenth transistor T13 has a gate adapted forreceiving the output signal O₃ of the stage S₃, a source electricallycoupled to the drain of the second transistor T2 of the pull-up circuit710 and a drain configured to receive the supply voltage VSS.

For the stage S₂, the circuit diagram is same as that of the stage S₁,except that the gate of the first transistor T1 of the pull-up controlcircuit 720 is adapted for receiving the output signal O₁ of the stageS₁. In the stage S₂, the source of the transistor T2 of the pull-upcircuit 710 is configured to receive the second clock signal C2, and thegate of transistor T4 of the first pull-down control circuit 740 isconfigured to receive the second supply voltage signal VDDb. The gatesof the transistors T12 and T13 of the third pull-down circuit 760 isconfigured to receive the output signal O₄ of the stage S₄.Additionally, the pull-down signal K₁ generated from the first pull-downcontrol circuit 740 of the stage S₁ is provided to the gates of thetransistors T9 and T10 of the second pull-down circuit 750 of the stageS₂.

FIG. 13 shows a timing chart of input and output signals for the shiftregister as shown in FIG. 12. ST is the start signal that is provided tothe gate of the transistor T1 of the pull-up control circuit 720 of thestage S₁. The clock signals C1, C2, C3 and C4 are provided to the sourceof the transistor T2 of the pull-up circuit 710 of the stages S₁, S₂, S₃and S₄, respectively. The frequency of each of the clock signals C1, C2,C3 and C4 is identical, while the phase of each of the clock signals C1,C2, C3 and C4 is sequentially shifted from each other. The first supplyvoltage signal VDDa is provided to the gate of the transistor T4 of thefirst pull-down control circuit 740 of the stages S₁ and S₃, while thesecond supply voltage signal VDDb is provided to the gate of thetransistor T4 of the first pull-down control circuit 740 of the stagesS₂ and S₄. The frequencies of the first supply voltage signal VDDa andthe second supply voltage signal VDDb are substantially identical, andthe phases of the first supply voltage signal VDDa and the second supplyvoltage signal VDDb are substantially reversed, respectively.

Signals O₁, O₂, O₃ and O₄ are respectively the output signals from thestages S₁, S₂, S₃ and S₄. Signal K₁ and K₂ are the pull-down signaloutput from the first pull-down control circuit 740 of the stages S₁ orS₂. Signals Q₁, Q₂, Q₃ and Q₄ are the voltage potentials at the node Q₁of the stage S₁, the node Q₂ of the stage S₂, the node Q₃ of the stageS₃ and the node Q₄ of the stage S₄, respectively.

FIG. 14 shows schematically a shift register 800 according to oneembodiment of the present invention. Similar to the shift register 600shown in FIG. 6, the shift register 800 has a plurality of stages,{S_(n)}, n=1, 2, . . . , N, which is electrically connected in serial.Each of the stages S₁, S₂, S₃ and S₄ is configured to receive acorresponding clock signal, C1, C2, C3 or C4, and a supply voltage, VDDaor VDDb, and responsively output an output signal, O₁, O₂, O₃ or O₄.Furthermore, each stage S₁, is also configured to receive the outputsignal O_(n−1) of the stage S_(n−1) and the output signal O_(n+2) of thestage S_(n+2). For example, the stage S₂ is electrically connected tothe stage S₁ and the stage S₂ for receiving the output signals O1 and O4therefrom, respectively. For the first stage S₁, a start signal, ST, isapplied thereto. However, in shift register 800, each stage S₂, S₃ or S₄outputs a corresponding pull-down signal K₁, K₂ or K₃ that is fedback toits immediately prior stage.

FIG. 15 shows a circuit diagram of the first and second stages S₁, S₂ ofa shift register 900 according to one embodiment of the presentinvention. The circuit of the shift register 900 is same as that ofshift register 700 as shown in FIG. 12, except that the pull-down signalK₁ generated from the first pull-down control circuit of the stage S₂ isprovided to the gates of the transistors T9 and T10 of the secondpull-down circuit of the stage S₁. For such a configuration, the timingchart of input and output signals for the shift register 900 are samethese shown in FIG. 13.

Referring to FIG. 16, a shift register 1000 is shown schematicallyaccording to one embodiment of the present invention. The shift register1000 has a plurality of stages, {S_(n)}, electrically connected inserial. In FIG. 16, only the first to fourth stages S₁, S₂, S₃ and S₄ ofthe shift register 1000 are shown. Each of the stages S₁, S₂, S₃ and S₄is configured to receive a corresponding clock signal, C1, C2, C3 or C4,and a supply voltage, VDDa or VDDb, and responsively output an outputsignal, O₁, O₂, O₃ or O₄. Furthermore, the stage S₁, is also configuredto receive the output signal O_(n−2) of the stage S_(n−2), (n=3 and 4).For example, the stage S₃ is electrically connected to the stage S₁ forreceiving the output signal O₁ therefrom. For the first and secondstages S₁ and S₃, a start signal ST is applied thereto. Additionally,each stage S₁, S₂, S₃ or S₄ also outputs a corresponding pull-downsignal K₁, K₂, K₃ or K₄, that is provided to its immediately next stage.

FIG. 17 shows a circuit diagram of the first and second stages S₁, S₂ ofa shift register 1100 according to an alternative embodiment of thepresent invention. The circuit of the shift register 1100 is same asthat of shift register 700 as shown in FIG. 12, except that the startsignal ST is applied to the gate of the transistor T1 of the pull-upcontrol circuit of the stage S₁ and S₂, respectively. For n=3, 4, 5, . .. , N, the output signal O_(n−2) is provided to the stage S_(n−2) isprovided to the gate of the transistor T1 of the pull-up control circuitof the stage S_(n).

FIG. 18 shows a timing chart of input and output signals for the shiftregister 1100 as shown in FIG. 17. ST is the start signal that isprovided to the gate of the transistor T1 of the pull-up control circuitof the stage S₁. The clock signals C1, C2, C3 and C4 are provided to thesource of the transistor T2 of the pull-up circuit of the stages S₁, S₂,S₃ and S₄, respectively. The frequency of each of the clock signals C1,C2, C3 and C4 is identical, while the phase of each of the clock signalsC1, C2, C3 and C4 is sequentially shifted from each other. The firstsupply voltage signal VDDa is provided to the gate of the transistor T4of the first pull-down control circuit of the stages S₁ and S₃, whilethe second supply voltage signal VDDb is provided to the gate of thetransistor T4 of the first pull-down control circuit of the stages S₂and S₄. The frequencies of the first supply voltage signal VDDa and thesecond supply voltage signal VDDb are substantially identical, and thephases of the first supply voltage signal VDDa and the second supplyvoltage signal VDDb are substantially reversed, respectively.

Signals O₁, O₂, O₃ and O₄ are respectively the output signals from thestages S₁, S₂, S₃ and S₄. Signal K₁, K₂ and K₂ are the pull-down signaloutput from the first pull-down control circuit of the stages S₁ S₂ andS₂. Signals Q₁, Q₂, Q₃ and Q₄ are the voltage potentials at the node Q₁of the stage S₁, the node Q₂ of the stage S₂, the node Q₃ of the stageS₃ and the node Q₄ of the stage S₄, respectively.

Referring to FIG. 19, a shift register 1200 is shown schematicallyaccording to one embodiment of the present invention. Similar to theshift register 1000 as shown in FIG. 16, the shift register 1200 hasfour stages S₁, S₂, S₃ and S₄, which are electrically connected inserial. Each of the stages S₁, S₂, S₃ and S₄ is configured to receive acorresponding clock signal, C1, C2, C3 or C4, and a supply voltage, VDDaor VDDb, and responsively output an output signal, O₁, O₂, O₃ or O₄.Furthermore, the stage S₁, is also configured to receive the outputsignal O_(n−2) of the stage S_(n−2), (n=3 and 4). For example, the stageS₃ is electrically connected to the stage S₁ for receiving the outputsignal O1 therefrom. For the first and second stages S₁ and S₃, a startsignal ST is applied thereto. However, in the shift register 1200, eachstage S₁, S₂, S₃ or S₄ outputs a corresponding pull-down signal K₁, K₂,K₃ or K₄, that is fedback to its immediately prior stage.

FIG. 20 shows a circuit diagram of the first and second stages S₁, S₂ ofa shift register 1300 according to another embodiment of the presentinvention. The circuit of the shift register 1200 is same as that ofshift register 1100 as shown in FIG. 17, except that the pull-downsignal K₁ generated from the first pull-down control circuit of thestage S₂ is provided to the gates of the transistors T9 and T10 of thesecond pull-down circuit of the stage S₁. For such a configuration, thetiming chart of input and output signals for the shift register are samethese shown in FIG. 18.

In sum, the present invention, among other things, discloses a shiftregister having a plurality of stages, {S_(n)}, n=1, 2, . . . , N, Nbeing a positive integer. Each pair of two neighboring stages S₁, andS_(n+1) or S_(n−1) and S₁, shares a single pull-down control circuit,Accordingly, it simplifies the GOA design and reduces the manufacturingcost of an LCD panel. Furthermore, it can reduce the stress and improvesthe reliability of operation of the LCD panel.

The foregoing description of the exemplary embodiments of the inventionhas been presented only for the purposes of illustration and descriptionand is not intended to be exhaustive or to limit the invention to theprecise forms disclosed. Many modifications and variations are possiblein light of the above teaching.

The embodiments were chosen and described in order to explain theprinciples of the invention and their practical application so as toenable others skilled in the art to utilize the invention and variousembodiments and with various modifications as are suited to theparticular use contemplated. Alternative embodiments will becomeapparent to those skilled in the art to which the present inventionpertains without departing from its spirit and scope. Accordingly, thescope of the present invention is defined by the appended claims ratherthan the foregoing description and the exemplary embodiments describedtherein.

1-28. (canceled)
 29. A shift register, comprising a plurality of stages,{S_(n)}, n=1, 2, . . . , N, N being a positive integer, wherein eachstage S_(n) comprises: (a) a pull-up circuit having an input forreceiving a corresponding clock signal Cn, an output for responsivelyoutputting an output signal, O_(n), and an input node, Q_(n), betweenthe input and the output; (b) a pull-up control circuit electricallycoupled to the input node Q_(n) of the pull-up circuit and configuredsuch that when receiving a first input signal, the pull-up controlcircuit responsively generates a signal that is identical to the firstinput signal and is provided to the input node Q_(n) of the pull-upcircuit to turn on the pull-up circuit; (c) a first pull-down circuitelectrically coupled to the input node Q_(n) and the output of thepull-up circuit and configured to receive a pull-down signal K_(n); (d)a second pull-down circuit electrically coupled to the input node Q_(n)and the output of the pull-up circuit, and configured to receive asecond input signal; (e) a third pull-down circuit electrically coupledto the input node Q_(n) and the output of the pull-up circuit andconfigured to receive a third input signal; and (f) a first pull-downcontrol circuit configured to receive a fourth input signal andresponsively generate the pull-down signal K_(n) that is provided to thefirst pull-down circuit of the stage S_(n) and the second pull-downcircuit of one of the stage S_(n−1) and the stage S_(n+1), respectively.30. The shift register of claim 29, wherein each of the clock signals{Cn}, n=1, 2, 3, . . . , N, is characterized with a frequency and aphase, wherein the frequencies of the clock signals {Cn} aresubstantially identical, and the phases of the clock signals {Cn} aresequentially shifted, respectively.
 31. The shift register of claim 30,wherein the fourth input signal is corresponding to a first supplyvoltage signal, VDDa, when n is an odd integer, or a second supplyvoltage signal, VDDb, when n is an even integer, wherein each of thefirst supply voltage signal VDDa and the second supply voltage signalVDDb is characterized with a frequency and a phase, wherein thefrequencies of the first supply voltage signal VDDa and the secondsupply voltage signal VDDb are substantially identical, and the phasesof the first supply voltage signal VDDa and the second supply voltagesignal VDDb are substantially reversed, respectively.
 32. The shiftregister of claim 31, wherein the second input signal is correspondingto the pull-down signal K_(n−1) of the stage S_(n−1) or the pull-downsignal K_(n+1) of the stage S_(n+1), wherein the third input signal iscorresponding to the output signal O_(n+2) of the stage S_(n+2),
 33. Theshift register of claim 31, wherein the first input signal iscorresponding to the output signal O_(n−1) of the stage S_(n−1) for n=2,3, 4, . . . , N, or a start signal for n=1.
 34. The shift register ofclaim 31, wherein the first input signal is corresponding to the outputsignal O_(n−2) of the stage S_(n−2) for n=3, 4, 5, . . . , N, or a startsignal for n=1 and
 2. 35. The shift register of claim 31, wherein thefirst input signal is corresponding to a start signal.